[N:1](/[C:4](=[CH:10]\[C:11]1[CH:19]=[CH:18][C:14]2[O:15][CH2:16][O:17][C:13]=2[CH:12]=1)/[C:5]([O:7][CH2:8][CH3:9])=[O:6])=[N+]=[N-]>C1(C)C(C)=CC=CC=1>[O:17]1[C:13]2=[CH:12][C:11]3[CH:10]=[C:4]([C:5]([O:7][CH2:8][CH3:9])=[O:6])[NH:1][C:19]=3[CH:18]=[C:14]2[O:15][CH2:16]1A stirred solution of (Z)-ethyl 2-azido-3-(benzo[d][1,3]dioxol-5-yl)acrylate (I-4a: 0.6 g, 1.532 mmol) in xylene (20 mL) was maintained at 150° C. for 3 h. Xylene was distilled out completely and the crude compound was purified by column chromatography over silica gel (100-200 mesh) using a solvent gradient of 8-10% ethyl acetate in petroleum ether as eluent to afford 0.4 g (75%) of ethyl 5H-[1,3]dioxolo[4,5-f]indole-6-carboxylate (I-4b) as a pale yellow solid.
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